Coloring the Biological World

Abstract

One enzyme has arguably caused more human strife than any other, the enzyme tyrosinase. The one shown here is from bacteria, but the one in our cells is similar but is bound to membranes. It performs an interesting reaction: it oxidizes the amino acid tyrosine, which then forms huge aggregates called melanin which strongly absorb light, looking dark brown or black. Cells in our skin have special compartments that make this melanin to help protect us from the dangerous effects of sunlight. Therein lies the problem. Human populations around the world have evolved cells that make different amounts and types of melanin, driven largely by their historical exposure to sunlight. This has yielded a beautiful diversity in skin color, ranging from clear white to darkest black and everything in between. Similar molecules give hair its shades of blonde, red, brown, and black. Unfortunately, human society has never been good with differences, and this highly visible consequence of a single enzyme has helped to fuel many of our current societal challenges.